The investigation of mechanisms involved in the tubular reabsorption of glutamate and other amino acids, and in the inhibitory action of heavy metals, will focus on 1) attempts to obtain a preparation which showed primarily tubular rather than glomerular lesions; this would permit the testing of effects of the metals on the kinetics of transmural movement of amino acids; 2) determination of kinetic constants describing transport of different amino acids in control and poisoned animals; this should lead to definition of the nature of the inhibition (i.e. non-competitive or uncompetitive). The implications of our findings on the nature of the reabsorption process in general will be analyzed.